1. Field of the Invention
This invention relates to tread-brake units for vehicles.
2. Description of the Prior Art
Tread-brake units are, of themselves, well known and comprise, as a unitary structure, a brake shoe for engagement with the tread of a vehicle wheel, a brake actuator having an output member via which the brake shoe can, firstly, be moved into engagement with the wheel tread and, thereafter, a braking force generated by the actuator can be transmitted to the brake shoe, and a slack adjuster by which clearance between the brake shoe and the wheel tread, in the "released" condition of the unit, can be maintained substantially constant.
The overall available envelope of tread-brake units is inevitably severely restricted as a result of their position on the vehicle and frequently the need for them to replace pre-existing units which may not incorporate slack adjusters. This restriction places considerable limitations on the space available on the unit to accommodate a slack adjuster and causes severe difficulties for designers.
One conventional and beneficial type of slack adjuster, as described in British Patent Specification No. 980881, includes a pair of fast-threaded nuts. One of these nuts is an "adjustment nut" and the other is "a force-transmitting nut". At various stages of operation of the slack adjuster these nuts are required to be clamped so as to be prevented from rotation on a common output member with which they are threadedly engaged. This is achieved with a tube encircling one or other or both of the nuts, which tube is held at an appropriate state in the operation of the slack adjuster against rotation. To provide such a tube in a tread-brake unit takes up space which, for the reasons given above, is at a premium in tread-brake units.